This invention relates to transferring information between telephones in an Integrated Services Digital Network (ISDN) and more particularly to the sharing and transferring of information between an ISDN telephone located at a users workplace (work at work telephone) and an ISDN telephone located in the users home (work at home telephone).
ISDN is capable of transferring data messages transparently between ISDN telephones. ISDN operates according to the call control methods and procedures defined by Bellcore in the National ISDN Technical Requirements. The Bellcore requirements specify information elements such as user-to-user information, calling sub-address information, and lower layer compatibility. ISDN also has the capability of sending X.25 data on the network. These information elements do not exist in any prior art analog service. ISDN basic rate service operates on a 2B+D configuration, that is, two 64 kilobyte per second B or bearer channels and one 16 kilobyte per second D or delta channel.
It has been proposed to use ISDN information elements to pass a calling party number received at a first ISDN telephone to a second ISDN telephone prior to transferring the call to the second telephone. See, for example, the patent to Kakwashima U.S. Pat. No. 5,422,942. One problem with this prior art call transfer method is that communication between the calling party and the second ISDN telephone is completed through the first ISDN telephone, occupying at least one channel of the first ISDN telephone until completion of the call.
The present invention proposes a method of transferring information between ISDN telephones that are operable in either a local or remote mode of operation. The telephones are placed in the local mode of operation when the user is available to accept calls and is placed in the remote operation mode if the user wishes incoming calls or other information to be transferred to a companion phone at a different location. The selection of the telephone mode of operation may be controlled either locally or from a remote location.
In accordance with the present invention, a telephone placed in a remote operation mode upon receipt of an incoming call, automatically inserts appropriate information such as calling line identification into a call origination function and shares that information with its companion telephone. The companion telephone uses the information to illuminate indicators, display messages and, if desired, request transfer of the incoming call. The present invention also provides a message waiting feature that notifies one of the telephones of any messages that have been left as a result of unanswered calls to the companion telephone. A common message waiting feature is also provided that permits a plurality of telephones to be informed of a waiting message that may be answered by a user at any one of the telephones.